December 29, 2015

Bronze Age people from Ireland had steppe ancestry and R1b

From the paper:

We were able to deduce that Neolithic Ballynahatty had a dark hair shade (99.5% probability), most likely black (86.1% probability), and brown eyes (97.3% probability) (46). Bronze Age Rathlin1 probably had a light hair shade (61.4%) and brown eyes (64.3%). However, each Rathlin genome possessed indication of at least one copy of a haplotype associated with blue eye color in the HERC2/OCA2 region.

and:

Third, we followed the methods described in Haak et al. (9), which use a collection of outgroup populations, to estimate the mixture proportions of three different sources, Linearbandkeramik (Early Neolithic; 35 ± 6%), Loschbour (WHG; 26 ± 12%), and Yamnaya (39 ± 8%), in the total Irish Bronze Age group. These three approaches give an overlapping estimate of ∼32% Yamnaya ancestry.

PNAS doi: 10.1073/pnas.1518445113

Neolithic and Bronze Age migration to Ireland and establishment of the insular Atlantic genome

Lara M. Cassidy, Rui Martiniano et al.

The Neolithic and Bronze Age transitions were profound cultural shifts catalyzed in parts of Europe by migrations, first of early farmers from the Near East and then Bronze Age herders from the Pontic Steppe. However, a decades-long, unresolved controversy is whether population change or cultural adoption occurred at the Atlantic edge, within the British Isles. We address this issue by using the first whole genome data from prehistoric Irish individuals. A Neolithic woman (3343–3020 cal BC) from a megalithic burial (10.3× coverage) possessed a genome of predominantly Near Eastern origin. She had some hunter–gatherer ancestry but belonged to a population of large effective size, suggesting a substantial influx of early farmers to the island. Three Bronze Age individuals from Rathlin Island (2026–1534 cal BC), including one high coverage (10.5×) genome, showed substantial Steppe genetic heritage indicating that the European population upheavals of the third millennium manifested all of the way from southern Siberia to the western ocean. This turnover invites the possibility of accompanying introduction of Indo-European, perhaps early Celtic, language. Irish Bronze Age haplotypic similarity is strongest within modern Irish, Scottish, and Welsh populations, and several important genetic variants that today show maximal or very high frequencies in Ireland appear at this horizon. These include those coding for lactase persistence, blue eye color, Y chromosome R1b haplotypes, and the hemochromatosis C282Y allele; to our knowledge, the first detection of a known Mendelian disease variant in prehistory. These findings together suggest the establishment of central attributes of the Irish genome 4,000 y ago.

This crushes the cherished theories by some on R1b spread. The paper found:

The very derived downstream clades of R1b like R1b1a2a1a2c were well-established in Ireland by 3750 before the present. There is no evidence the ancient specimens in the paper were the first generation in Ireland, so it is likely they were present by 2000 BCE.

2. The population of the Central European migrants to Ireland, who were herders, and had some Steppe-derived ancestry, were MUCH higher, compared to hunter gatherers. In other words, R1b is so common in Ireland because of massive migration of such people.

3. This is emphatically NOT consistent with pioneer colonization and elite dominance.

4. The current high R1b distributions in many parts of Western Europe and certainly Ireland are due to a LACK of invasions since (no Anglo-Saxon or Roman penetration.) In other words, this was a second but more prounounced founder effect of sorts.

5. This is consistent with comparisons to more centrally located, easy to reach locales, like Italy, where the genomes show greater variability in both autosomes and Y DNA, due to introgressions that occurred after the late Neolithic and early Bronze Age migrations. (Cavalli-Sforza's admonishment to understand the difference between an expansion and an "impansion" come to mind.)

6. In Western Europe, Bell Beaker culture is the most likely candidate for the spread of R1b and related autosomal genes.

7. R1b and this Western European expansion is strongly scientifically correlated to lactose persistence, which likely provided the demographic advantage to propagate in larger numbers in places like Hibernia.

8. As an addendum, the megaliths of Western Europe are indeed likely linked to early cardial cultures, who bore of mix of HG and farming genes, which correlate to I-M26 in Ireland and Sardinia.

Xaver: the contribution to Bell Beaker was probably also from some "cousinelike" folks, because Yamnaya R1b is not upstream to their R1b (nor to the newly found BA Irish R1b). So the source is at least not the Volga-Yamnaya group that represents the Yamnaya yDNA currently.

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